Structure and method for 3D image sensor

ABSTRACT

The present disclosure provides an embodiment of an image sensor structure that includes a first semiconductor substrate having a plurality of imaging sensors; a first interconnect structure formed on the first semiconductor substrate; a second semiconductor substrate having a logic circuit; a second interconnect structure formed on the second semiconductor substrate, wherein the first and the second semiconductor substrates are bonded together in a configuration that the first and second interconnect structures are sandwiched between the first and second semiconductor substrates; and a backside deep contact (BDCT) feature extended from the first interconnect structure to the second interconnect structure, thereby electrically coupling the logic circuit to the image sensors.

CROSS-REFERENCE

This application claims the benefit of U.S. Provisional Application61/799,113 entitled “3D CMOS IMAGE SENSOR,” filed Mar. 15, 2013, hereinincorporated by reference in its entirety.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. In the course of ICevolution, functional density (i.e., the number of interconnecteddevices per chip area) has generally increased while geometry size(i.e., the smallest component or line that can be created using afabrication process) has decreased. This scaling down process generallyprovides benefits by increasing production efficiency and loweringassociated costs.

As one application, imaging sensors are incorporated in an integratedcircuit. The existing imaging sensor has logic and pixel array on thesame Si wafer and another wafer is a carrier only. Various issues maypresent in the existing imaging sensor structure. In one example,process tuning to image sensors impacts logic circuit area. In anotherexample, small pixel layout suffers low quantum efficiency (QE) and fullwell capacity (FWC) due to devices occupancy. In yet another example,image signal processor (ISP) seizes a larger layout area, leading to lowgross die count per unit area.

Therefore, what is needed is a structure for imaging sensor and methodmaking the same to address the above issues.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with accompanying figures. It is emphasized that,in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposeonly. In fact, the dimension of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIGS. 1 and 2 illustrate an imaging sensor structure in a top view and aschematic view, respectively, constructed according to variousembodiments.

FIG. 3 illustrates a schematic view of the imaging sensor structureconstructed according to another embodiment.

FIG. 4 illustrates a schematic view of the imaging sensor structureconstructed according to another embodiment.

FIG. 5 is a flowchart of a method making the imaging sensor structureconstructed according to one or more embodiment.

FIGS. 6 and 7 illustrate sectional views of a logic circuit chip atvarious fabrication stages constructed according to one or moreembodiment.

FIG. 8 illustrates a schematic view of the logic circuit structure andan image sensor chip constructed according to one embodiment.

FIGS. 9-14 illustrate sectional views of the imaging sensor structure atvarious fabrication stages constructed according to one or moreembodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the disclosure.Specific examples of components and arrangements are described below tosimplify the present disclosure. These are, of course, merely examplesand are not intended to be limiting. For example, the formation of afirst feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

The present disclosure provides an imaging sensor structure and themethod making the same with improved pixel performance, increased grossdie count and enhanced image signal processor (ISP) function.

FIG. 1 illustrates a top view of an image sensor structure 10 and FIG. 2illustrates a schematic view of the image sensor structure 10. The imagesensor structure 10 has a three dimensional (3D) structure that includesa first integrated circuit (IC) chip 12 and a second IC chip 14. The ICsubstrate 14 is stacked on, mechanically bonded to, and electricallycoupled with the first IC chip 12. The first IC chip 12 is designed andconfigured to form various image sensors and the second IC chip 14 isdesigned and configured to form various driving circuit and logicdevices to the image sensors. The first and second IC chips are alsoreferred to as image sensor chip and logic circuit chip, respectively.

The first IC chip 12 includes a first substrate. In one embodiment, thefirst substrate includes silicon. The first substrate may additionallyor alternatively include some other suitable elementary semiconductor,such as diamond or germanium; a suitable compound semiconductor, such assilicon carbide, indium arsenide, or indium phosphide; or a suitablealloy semiconductor, such as silicon germanium carbide, gallium arsenicphosphide, or gallium indium phosphide.

The first IC chip 12 includes various doped regions, and other featuresconfigured to form image sensors that are sensitive to photon or otherimage radiation. In one embodiment, the image sensors includephotodiodes, such as complementary metal-oxide-semiconductorfield-effect transistor (CMOSFET)-based photodiodes or otherphotosensitive devices. In one embodiment, those image sensors arefurther configured to form an image sensor array for variousapplications including imaging. In one example, the image sensors arebackside illuminated CMOSFET-based image sensors, where the illuminationbeam is received from the backside of the image sensors. Accordingly,the first IC chip 12 is also referred to as image sensor chip 12. Thefirst IC chip 12 includes conductive material features and dielectricmaterial features disposed on the first substrate and configured forcoupling and isolating various microelectronic components, respectively.As one example, the first IC chip 12 includes one or more materiallayers, such as interleave dielectric material layers (ILDs) and metallayers that are embedded in the ILDs and are patterned to form metallines, vias and contacts. In another embodiment, the first IC chip 12may further include other microelectronic devices.

The second IC chip 14 includes a second substrate. In the presentembodiment, the second substrate is substantially similar to the firstsubstrate. In one example, the second substrate includes silicon. Inother examples, the second substrate alternatively or additionallyincludes some other suitable elementary semiconductor, a suitablecompound semiconductor, or a suitable alloy semiconductor.

The second IC chip 14 includes various microelectronic devices, such asCMOSFET-based logic devices and circuits. Particularly, the second ICchip 14 includes various microelectronic devices configured to formdriving circuits/devices for the image sensors. In one embodiment, thedriving circuits to the image sensors include address lines and datalines to the image sensor array. The driving circuits to the imagesensors further include driving devices reset (RST) device, sourcefollower (SF), and row selector (RS). In the present embodiment, thosedriving devices are configured in group to be coupled with one pixel ofthe image sensors or a subset of the pixels. Various circuits anddevices formed in the second IC chip 14 are collectively referred to aslogic devices in the later description. In one example, the second ICchip is an application-specific integrated circuit (ASIC) chip.

The first IC chip 12 and the second IC chip 14 are mechanically bondedtogether through a suitable bonding mechanism, such as fusion bonding,eutectic bonding or other suitable bonding technique. The first IC chip12 and the second IC chip 14 are electrically coupled together throughbackside deep contact (BDCT) features. The BDCT features are formed inthe deep trenches in the interconnect structure of the first IC chip 12,are further extended to the interconnect structure of the second IC chip14, are configured with other conductive features to electrically coupletogether the driving devices in the second IC chip 14 and the imagesensors in the first IC chip 12. The BDCT features will be furtherdescribed later in terms of the formation and configuration. Since theimage sensors and the corresponding driving circuits/devices aredistributed into two IC chips (12 and 14 in the present embodiment),there are more freedom and flexibility to reconfigure and tune the imagesensors and the driving circuits/devices for improved performance andefficiency. For example, the image sensors and the logic devices areindividually tuned for their performance during the respectivefabrication operations before bonding and coupling together. In thepresent embodiment, the 3D image sensor structure 10 is formed by aprocedure where the first IC chip 12 and the second IC chip 14 arefabricated and bonded in wafer level and thereafter are diced toseparate a plurality of the 3D image sensor structures 10.

FIG. 3 illustrates a schematic view of the 3D image sensor structure 10constructed according to aspects of the present disclosure in anotherembodiment. The 3D image sensor structure 10 includes the first IC chip12 and the second IC chip 14 mechanically bonded together andelectrically coupled with each other. The first IC chip 12 is designedand configured to form various image sensors and the second IC chip 14is designed and configured to form various logic circuits that includedriving circuit/devices to the image sensors.

The first IC chip 12 includes a first substrate 16. In one embodiment,the first substrate includes silicon. The first substrate mayadditionally or alternatively include some other suitable elementarysemiconductor; a suitable compound semiconductor; or a suitable alloysemiconductor.

The first IC chip 12 includes various doped regions, and other featuresconfigured to form image sensors 18 that are sensitive to photon orother image radiation. In one embodiment, the image sensors 18 includephotodiodes, such as CMOSFET-based photodiodes or other photosensitivedevices. In one example, the image sensors are backside illuminatedCMOSFET-based image sensors. In the present embodiment, the first ICchip 12 also includes other features, such as transfer gates (“TX” inFIG. 3) formed on the photodiodes 18, respectively. The first IC chip 12includes an interconnect structure (also referred to as a firstinterconnect structure) formed on the first substrate 16. The firstinterconnect structure includes metal lines, vias and contacts toprovide horizontal and vertical electrical routing. The interconnectstructure may include a plurality of metal layers, such as a first metallayer (“M1”), a second metal layer (“M2”), . . . and so on. The firstinterconnect structure includes various conductive features configuredto an electrical routing 20 to provide electrical routing to thetransfer gates.

The second IC chip 14 includes a second substrate 22. In the presentembodiment, the second substrate 22 is substantially similar to thefirst substrate 16. For examples, the second substrate includes silicon.

The second IC chip 14 includes various microelectronic devices, such asCMOSFET-based logic devices formed on the second substrate 22.Particularly, the second IC chip 14 includes various microelectronicdevices configured to drive the image sensors 18. In one embodiment, thedriving devices to the image sensors include reset (RST) device, sourcefollower (SF), and row selector (RS). In the present embodiment, thosedriving devices are configured in pixel levels such that a group ofthose devices are coupled with one pixel of the image sensors 18 or asubset of pixels in the image sensor array. Accordingly, the couplingbetween the driving devices to the image sensors are pixel-based and theconductive features to connect both need to be properly designed andconfigured to provide such capability with chip area efficiency.

The second IC chip 14 also includes an interconnect structure (alsoreferred to as a second interconnect structure) formed on the secondsubstrate 22. The second interconnect structure includes a plurality ofmetal layers, such as a first metal layer, a second metal layer, . . .and the top metal (“TM”). One of the metal lines in the top metal layeris illustrated in FIG. 3.

The first IC chip 12 and the second IC chip 14 are mechanically bondedtogether through a suitable bonding mechanism. The first IC chip 12 andthe second IC chip 14 are electrically coupled together through one ormore backside deep contact (“BDCT” in FIG. 3) feature. The BDCT featureis formed in the deep trenches in the interconnect structure of thefirst IC chip 12, further extended to the interconnect structure of thesecond IC chip 14, and configured with other conductive features toelectrically couple together the driving devices in the second IC chip14 and the image sensors 18 in the first IC chip 12.

The BDCT feature has a small dimension in a top view toward the first orsecond substrate since it is pixel-based with small footprint. In oneexample, the dimension of the BDCT feature is less than 1 micron.Particularly, the BDCT feature is extended from the contact feature 24of the first interconnect structure in the first substrate 16 to aconductive feature (referred to as “BSSI” feature in FIG. 3) formed inthe second substrate 22. The BSSI feature is embedded in the secondsubstrate 22 and formed by backside silicon (BSSI) etch. The BDCTfeature is extended through a first metal line in the first metal layer(“M1”) and a second metal line in the top metal (“TM”) layer of thesecond interconnect structure. In the present embodiment, the BDCT hasdifferent dimensions in different portions. The BDCT includes a firstportion between the BSSI feature and the second metal line, and a secondportion between the second metal line and the first metal line. Thefirst portion has a first dimension (first width) and the second portionhas a second dimension (second width) greater than the first dimension,as illustrated in FIG. 3. This structure can be achieved by a procedureincluding multiple etchings.

As noted above, the image sensors and the corresponding driving devicesare respectively formed on two IC chips, with more freedom andflexibility to reconfigure and tune the image sensors and the drivingdevices for improved performance and efficiency. One such example of the3D image sensor structure 10 is illustrated in FIG. 4 in a schematicallytop view. The 3D image sensor structure 10 includes photodiodes (“PD”)and transfer gates (“TX”) formed on the first IC chip. The first IC chipis mechanically bonded and is further electrically coupled with thesecond IC chip through the BDCT feature and BSSI feature. The BDCT andBSSI features are formed by a 3D procedure on the backside of the secondIC chip, which will be further described later. The signal lines 20 andthe ground line 30 to the photodiodes are configured on the pixel edgesand are electrically coupled to the logic circuit/devices through BDCTfeature in the 3D connection.

FIG. 5 is a flowchart of a method 40 making the 3D image sensorstructure 10, and FIGS. 6-13 illustrates the 3D image sensor structure10 at various fabrication stages constructed according one or moreembodiment. As one embodiment, the present method 40 is implemented inwafer-level with more efficiency and various 3D image sensor chips areseparated by dicing after the bonding and the formation of theelectrical coupling features.

Referring to FIGS. 5 and 6, the method 40 begins at operation 42 byproviding the second IC structure (logic circuit wafer in the presentembodiment) 14. In the present embodiment, the second IC structure 14 isan ASIC chip and has a semiconductor-on-insulator (SOI) structure.Particularly, the second IC structure 14 includes a semiconductorsubstrate 22 (such as a silicon wafer) having an embedded a dielectricmaterial layer 62. In the present example, the dielectric material layer62 is a silicon oxide layer. The SOI structure of the second ICstructure 14 is formed by a suitable technique, such as separation byimplanted oxygen (SIMOX) or a procedure including oxidation, waferbonding and thin-down. The semiconductor substrate 22 is separated totwo portions an upper portion 22A and a lower portion 22B by thedielectric layer 62. The upper portion 22A functions as an activeportion and various logic devices are formed in the upper portion 22A.For example, source and drain features of the CMOSFETs are formed in theupper portion 22A of the substrate 22.

The second IC structure 14 includes various logic devices formed on thesubstrate 22. The logic devices include CMOSFET-based devices thatinclude the driving devices, such as RST, SF and RF, to be coupled tothe image sensors.

The second IC structure 14 includes an interconnect structure 64 formedon the substrate 22. The interconnect structure 64 includes variousmetal lines (in respective metal layers), vias and contacts configuredto provide electrical routing. The formation of the interconnectstructure 64 includes a suitable procedure, such as damascene processfor copper connection. In this method, the interlayer dielectricmaterial layer is deposited, and patterned to form trenches usinglithography process and etch. The metal, such as copper, is deposited tofill in the trenches and is further polished for removing excessiveportion and planarizing the top surface by chemical mechanical polishing(CMP). The metal deposited to the trenches may include barrier layer(such as titanium nitride or tantalum nitride) by physical vapordeposition (PVD), copper seed layer by PVD and bulk copper by plating.In FIG. 6, metal features 66 in the top metal layer are illustrated.

Referring to FIGS. 5 and 7, the method 40 proceeds to operation 44 byperforming an ion implantation to the substrate 22, thereby forming animplanted layer 68 in the interface between the dielectric layer 62 andthe lower portion 22B of substrate 22, as illustrated in FIG. 7. In thepresent embodiment, the implantation species is hydrogen. The ionimplantation process is tuned with various parameters including dose andenergy in order to achieve a smart cut at a later fabrication stage.Particularly, the ion implantation process is applied to the substrate22 without using an implantation mask to block certain areas since it isnot intended to form a portion of the logic circuit. Instead, it isintended to achieve the smart cut.

Referring to FIGS. 5, 8 and 9, the method 40 proceeds to operation 46 bybonding the second IC structure (logic circuit wafer) 14 to the first ICstructure (image sensor wafer) 12 together, resulting in a bonded 3Dimage sensor structure 10. The first IC structure 12, as describedabove, includes a plurality of photosensitive devices, such asphotodiodes, formed thereon. The image sensor structure 12 includes asemiconductor substrate 16, such as a silicon wafer. The image sensorstructure 12 includes a first interconnect structure 69 having variousmetal lines, vias and contacts. A metal line 70 in the first metal layerof the first interconnect structure is illustrated in FIG. 9. Thebonding process is designed to bond the two IC chips in a configurationsuch that the first interconnect structure of the first IC structure 12and the second interconnect structure of the second IC structure 14 aresandwiched between the two substrates 16 and 22. The bonding process mayimplement a suitable bonding mechanism, such as fusion bonding, eutecticbonding, or other boning technique.

Still referring to FIGS. 5 and 9, the method 40 proceeds to operation 48by separating the lower portion 22B of the second substrate 22 from the3D image sensor structure 10 by an annealing procedure. In the presentembodiment, the annealing procedure includes a two-phase annealing: afirst annealing and a second annealing. The first annealing is designedto separate the lower portion 22B of the second substrate 22.Particularly, the first annealing includes an annealing temperature ofabout 500° C. The first annealing causes the crystalline rearrangementand coalescence of the implanted layer 68. During the first annealing,the micro cavities in the implanted layer 68 are growing in sizes andthe pressure builds up in the growing cavities, causing the lowerportion 22B split from the 3D image sensor structure 10.

The second annealing is designed to enhance the bonding strength betweenthe first and the second IC structures 12 and 14. In the presentembodiment, the second annealing has a second annealing temperature ofabout 1100° C.

Referring to FIGS. 5 and 10, the method 40 proceeds to operation 50 bypolishing the second substrate 22 from the backside. In the presentembodiment, the dielectric layer 62 is removed and the correspondingoutside surface is planarized by polishing, such as by CMP.

Referring to FIGS. 5 and 11, the method 40 proceeds to operation 52 bypatterning the second substrate 22 to form (one or more) opening thatdefines the region for the BDCT feature. Specifically, the upper portion22A of the second substrate 22 is patterned to form a through opening 72such that the second interconnect structure is exposed within theopening 72. The patterning process includes a lithography process andetching. In one example, the lithography process includes coatingphotoresist layer on the upper portion 22A; performing a lithographyexposure to the photoresist layer; and developing the exposedphotoresist layer to form a patterned photoresist layer. The etching isdesigned to selectively etch the upper portion 22A of the secondsubstrate 22 (selectively etch silicon in the present embodiment wherethe upper portion 22A includes silicon). In another embodiment ofpatterning the second portion 22A, a hard mask may be employed. Forexample, a hard mask layer is deposited on the upper portion 22A, apatterned photoresist layer is formed by a lithography process, anetching process is applied to the hard mask layer using the patternedphotoresist layer as an etch mask, and thereafter, another etchingprocess is applied to the upper portion 22A using the patterned hardmask layer as an etch mask. In another example, the lithography processmay include other suitable technologies, such as ultraviolet (UV)lithography, deep UV (DUV) lithography, extreme UV (EUV) lithography, orelectron-beam lithography. In yet another example, the lithographyprocess may be replaced by other suitable technologies, such asmolecular imprint or maskless lithography.

Referring to FIGS. 5 and 12, the method 40 proceeds to operation 54 byforming one or more deep interconnect trench 74 for backend deepcontact. The deep interconnect trench 74 vertically extends from thesecond IC structure 14 to the first IC structure 12. Especially, thedeep interconnect trench 74 extends from the second interconnectstructure of the second IC structure 14 to the first interconnectstructure of the first IC structure 12. The deep interconnect trench 74includes a first trench portion and a second trench portion withdifferent dimensions. The first trench portion vertically spans betweenthe metal line 70 in the first metal layer of the first interconnectstructure and the metal line 66 in the top metal layer of the secondinterconnect structure. The second trench portion is in the second ICstructure and vertically spans from the metal line 66 in the top metallayer of the second interconnect structure to the second substrate 22.In the present example, the first trench portion has a first horizontaldimension (first trench width) W1 and the second trench portion has asecond horizontal dimension (second trench width) W2 greater than W1,thereby providing more room for the image sensors in the first IC chip12.

The deep interconnect trench 74 is aligned with the metal lines 66 and70, and therefore electrically couple the metal lines 66 and 70 togetherby the BDCT feature to be formed, thereby providing the electricalinterconnection between the first and second IC chips, particularlyproviding the electrical interconnection between the image sensors inthe first IC structure 12 and the logic devices in the second ICstructure 14.

The formation of the deep interconnect trench 74 includes variousetching processes. Since the second interconnect structure includesvarious metal features formed in one or more interlayer dielectric (ILD)material layers. The ILD material layers includes a suitable dielectricmaterial, such as silicon oxide, silicon nitride, silicon oxynitride,polyimide, spin-on glass (SOG), fluoride-doped silicate glass (FSG),carbon doped silicon oxide, and low k dielectric material. The etchingprocesses are designed to selectively etch the ILD material layers.

In one embodiment, the formation of the deep interconnect trench issimilar to the dual damascene process, such as via-first dual damasceneprocess, trench-first dual damascene process or other suitable dualdamascene process. In furtherance of the embodiment, the metal lines 66and 70 may serve as etch stop layers in the etch processes to form thefirst and second trench portions, respectively.

The formation of the deep interconnect trench 74 in a particular exampleis described below. The first etch process is applied to the ILD layersto form the second trench portion of the deep interconnect trench 74through the opening 72 in the upper portion 22A of the second substrate22 using the upper portion 22A as an etch mask. The opening 72 may beexpanded to a large size during the first etch process. The first etchprocess is designed with an etchant to selectively remove the dielectricmaterial of the ILD material layers and to stop on the metal line 66. Asecond etch process is applied to the metal line 66 to open the metalline 66 within the trench. Thereafter, a processing procedure includinglithography process and etch is applied to form the first trenchportion. In the processing procedure, a patterned photoresist layer isformed on the upper portion 22A of the second substrate 22 and in thesecond trench portion by a lithography process. The lithography processincludes photoresist coating, exposure and developing, and may furtherinclude various baking steps, such as soft baking, post exposure bakingand hard baking. The patterned photoresist layer includes an openingthat defines the region for the first trench portion. A third etchingprocess is applied to etch the ILD dielectric material layer of thesecond interconnect structure and the ILD dielectric material layer ofthe first interconnect structure. In one example, the third etchingprocess is similar to the first etching process in terms of the etchantand etches selectivity. In furtherance of the example, the third etchingprocess stops on the metal line 70. Other suitable procedure that isable to form the deep interconnect trench 74 may be implemented. Forexample, additional etch stop layer may be formed on the metal lines 70(or 66) to stop the corresponding etch process for forming the firsttrench portion (or the second trench portion), to enhance the etchcontrol.

Referring to FIGS. 5 and 13, the method 40 proceeds to operation 56 byforming the BDCT feature 76. In one embodiment, the formation of theBDCT feature 76 is similar to the formation of metal features by thedual damascene process. In furtherance of the embodiment, the formationof the BDCT feature 76 includes filling the deep interconnect trench 74with one or more conductive material; and performing a chemicalmechanical polishing (CMP) process to remove the excessive metaldeposited on the substrate 22A and planarize the top surface. In variousexamples, the conductive material includes metal or metal alloy, such ascopper, tungsten, metal silicide, aluminum or other suitable conductivematerial. In another example, the conductive material may include morethan one material layers. The conductive material may be deposited by asuitable technique, such as physical vapor deposition (PVD), plating,chemical vapor deposition (CVD). In the present example, the BDCTfeature 76 includes a barrier layer, such as titanium nitride ortantalum nitride deposited by PVD; a copper seed layer formed on thebarrier layer by PVD; and bulk copper to fill in the deep interconnecttrench by plating.

In the present embodiment, during the formation of the BDCT feature 76,the opening 72 of the substrate 22A is also filled with the conductivematerial, thereby forming another conductive portion in the opening 72.The portion of the conductive material in the opening 72 is collectivelylabeled by numeral 76 in FIG. 13 (it is also referred to as the BSSIfeature in FIG. 3).

Additionally, a passivation layer 78 is formed on the substrate 22A andthe BDCT feature 76. The passivation layer 78 includes a suitablematerial for passivation, such as a silicon oxide layer, a siliconnitride or a combination thereof, formed by a suitable method, such CVD.

Referring to FIGS. 5 and 14, the method 40 may include an operation 58by bonding a carrier substrate 80 (such as another silicon wafer) to the3D image sensor structure 10 if it is too thin without enough mechanicalstrength. In one example, the upper portion 22A of the second substrate22 is too thin. The carrier substrate 80 is boned to the secondsubstrate to the passivation layer 80 by a suitable bonding mechanism,such as fusion bonding or eutectic bonding. In another embodiment, afterthe bonding of the carrier substrate 80, the first substrate 16 isthinned down from the backside such that the thickness of the firstsubstrate 16 is substantially reduced. Thereby, the image sensors formedin the first substrate 16 are able to receive image light moreefficiently with reduced energy loss.

The method 40 may further include other operations to complete theformation of the 3D image sensor structure 10. In one example, themethod 40 may include forming various features to enhance the imagingeffect of the image sensors, such as forming color filter andmicro-lenses on the backside of the first substrate. In another example,the method 40 may include a dicing process to form a plurality of 3Dimage sensor chips when the above operations are implemented in waferlevel.

The present disclosed 3D image sensor structure and the method makingthe same are described in various embodiments. Other alternativeembodiments may present without departure from the spirit of the presentdisclosure. In one embodiment, the carrier wafer as the third substratebonded to the 3D image sensor structure includes other logic circuit forfurther ISP function enhancement. For example, various logic devicesincluding the driving devices to the image sensors are properlydistributed in the logic substrate and the carrier wafer for moreconfiguration freedom and design flexibility to enhance the performanceof the 3D image sensor structure. In another embodiment of the disclosedstructure and method, the driving devices to the image sensors arerelocated on the logic substrate for image sensor performanceimprovement, such as the enlargement of quantum efficiency (QE) and fullwell capacity (FWC). In yet another embodiment, the image sensors in the3D image sensor structure may be replaced by other sensors to employ theadvantages of the 3D structure. In yet another embodiment, the metalline 70 of the 3D image sensor structure 10 may be a metal line inanother metal layer, such as second metal layer.

Different advantages may present in various embodiments. In oneembodiment, image sensor pixel performance is improved through afine-tuning process regardless of logic circuit since the logic circuitis independently formed in the logic circuit wafer before bonding to theimage sensor wafer. Accordingly, gross dies (the number of working dies)increases relative to those in the existing approach. Other advantagesincludes ISP function enhancement, and easy to extend to next generationprocess in various embodiments.

Thus, the present disclosure provides an embodiment of an image sensorstructure. The image sensor structure includes a first semiconductorsubstrate having a plurality of imaging sensors; a first interconnectstructure formed on the first semiconductor substrate; a secondsemiconductor substrate having a logic circuit; a second interconnectstructure formed on the second semiconductor substrate, wherein thefirst and the second semiconductor substrates are bonded together in aconfiguration that the first and second interconnect structures aresandwiched between the first and second semiconductor substrates; and abackside deep contact (BDCT) feature extended from the firstinterconnect structure to the second interconnect structure, therebyelectrically coupling the logic circuit to the image sensors.

The present disclosure also provides another embodiment of a threedimensional (3D) image sensor structure. The 3D image sensor structureincludes a first integrated circuit (IC) chip having a plurality ofimaging sensors formed in a first silicon substrate and a firstinterconnect structure formed on the first silicon substrate; a secondIC chip having a logic circuit formed in a second silicon substrate anda second interconnect structure formed on the second silicon substrate,wherein the first and second IC chips are mechanically bonded togetherin a configuration that the first and second interconnect structures aresandwiched between the first and second silicon substrates; and abackside deep contact (BDCT) feature extended from the firstinterconnect structure to the second interconnect structure, therebyelectrically coupling the logic circuit to the image sensors.

The present disclosure also provides one embodiment of a method forfabricating a three dimensional (3D) image sensor structure. The methodincludes providing a logic substrate having a logic circuit formedtherein and a first interconnect structure formed thereon, wherein thelogic substrate has a silicon on insulator (SOI) structure; performing ahydrogen ion implantation process to the logic substrate, therebyforming a hydrogen implanted layer in the logic substrate; bonding thelogic substrate to an image sensor substrate having image sensors formedtherein and a second interconnect structure formed thereon; performingan annealing process, thereby achieving a smart cut to the logicsubstrate; performing an etching process to form a deep interconnecttrench continuously extending from the logic substrate to the firstinterconnect structure; and forming a backside deep contact (BDCT)feature in the deep interconnect trench, thereby electrically couplingthe logic circuit to the image sensors.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. An image sensor structure, comprising: a firstsemiconductor substrate having a plurality of imaging sensors, the firstsemiconductor substrate having a first side and an opposing second side;a first interconnect structure formed on the first side of the firstsemiconductor substrate; a second semiconductor substrate having a logiccircuit, the second semiconductor substrate having a third side and anopposing fourth side; a second interconnect structure formed on thethird side of the second semiconductor substrate, wherein the first andthe second semiconductor substrates are bonded together in aconfiguration that the first side of the first semiconductor substratefaces the third side of the second semiconductor substrate such that thefirst and second interconnect structures are sandwiched between thefirst and second semiconductor substrates; and a backside deep contact(BDCT) feature extended from the fourth side of the second semiconductorsubstrate through the third side of the second semiconductor substrateand the second interconnect structure, to the first interconnectstructure, thereby electrically coupling the logic circuit to the imagesensors.
 2. The image sensor structure of claim 1, wherein the BDCTfeature extends from the second interconnect structure to the firstinterconnect structure in a first direction; and the BDCT featureincludes a dimension less than about 1 micron in a second directionorthogonal to the first direction.
 3. The image sensor structure ofclaim 2, wherein the first interconnect structure includes a first metallayer having a first metal line; the second interconnect structureincludes a top metal layer having a second metal line; and the BDCTfeature extends through the second metal line and contacts the firstmetal line.
 4. The image sensor structure of claim 3, wherein the BDCTfeature includes a first portion having a first width and a secondportion having a second width greater than the first width; the firstportion extends from the first metal line to the second metal line; andthe second portion extends from the second metal line to the secondsemiconductor substrate.
 5. The image sensor structure of claim 2,wherein the BDCT feature includes a conductive material layer selectedfrom the group consisting of copper, tungsten, metal silicide, aluminum,and a combination thereof.
 6. The image sensor structure of claim 1,wherein the image sensors include photodiodes; and the logic circuitincludes driving devices to drive the image sensors.
 7. The image sensorstructure of claim 6, wherein the image sensors further include transfergates formed on and coupled with the photodiodes, respectively; and thedriving devices includes a reset (RST) device, a source follower (SF)and a row selector (RS).
 8. The image sensor structure of claim 1,further comprising a conductive feature formed in the secondsemiconductor substrate and contacting the BDCT feature.
 9. The imagesensor structure of claim 1, wherein the image sensors includes a subsetof the image sensors configured around the BDCT feature.
 10. The imagesensor structure of claim 1, further comprising a third semiconductorsubstrate bonded to the second semiconductor substrate, wherein thefirst, second and third semiconductor substrates are silicon substrates.11. A method for fabricating a three dimensional (3D) image sensorstructure, comprising: providing a logic substrate having a logiccircuit formed therein and a first interconnect structure formedthereon, wherein the logic substrate has a silicon on insulator (SOI)structure; performing a hydrogen ion implantation process to the logicsubstrate, thereby forming a hydrogen implanted layer in the logicsubstrate; bonding the logic substrate to an image sensor substratehaving image sensors formed therein and a second interconnect structureformed thereon; performing an annealing process, thereby achieving asmart cut to the logic substrate; performing an etching process, therebyforming a deep interconnect trench continuously from the logic substrateto the first interconnect structure; and forming a backside deep contact(BDCT) feature in the deep interconnect trench, thereby electricallycoupling the logic circuit to the image sensors.
 12. The method of claim11, wherein the SOI structure of the logic substrate includes a firstsilicon layer and a second silicon layer interposed by a silicon oxidelayer, wherein the logic circuit is formed in the first silicon layer,the first interconnect structure is formed on the first silicon layer,the hydrogen implanted layer formed in the second silicon layer adjacentthe silicon oxide layer; and the annealing process includes a firstannealing with a first annealing temperature to separate the secondsilicon layer from the logic substrate, and thereafter a secondannealing with a second annealing temperature greater than the firstannealing temperature.
 13. The method of claim 12, further comprising:performing a polishing process to the logic substrate, thereby removingthe silicon oxide layer, after the performing of the annealing processand before the forming of the BDCT feature.
 14. The method of claim 13,wherein the forming of the BDCT feature includes: patterning the firstsilicon layer of the logic substrate to form a first opening through thefirst silicon layer; performing a first etching process to the firstinterconnect structure within the first opening, thereby forming a firstinterconnect trench that exposes a first metal line of a top metal layerin the first interconnect structure; patterning the first metal line,thereby forming a second opening through the first metal line;performing a second etching process within the second opening, therebyforming a second interconnect trench that extends to a second metal lineof a first metal layer in the second interconnect structure; filling thefirst and second interconnect trench with a conductive material, therebyforming the BDCT feature in the first and second interconnect trenches;and performing a chemical mechanical polishing (CMP) to the logicsubstrate, thereby removing excessive portion of the conductivematerial.
 15. The method of claim 14, further comprising: forming apassivation layer on the logic substrate; bonding a carrier substrate tothe passivation layer; and thinning down the image sensor substrate. 16.A method comprising: performing a hydrogen ion implantation process on afirst substrate to form a hydrogen layer in the logic substrate, whereinthe first substrate includes a logic device electrically coupled to afirst interconnect structure formed thereon; coupling the firstsubstrate to a second substrate, wherein the second substrate includesan image sensor electrically coupled to a second interconnect structureformed thereon; annealing the first substrate to thereby remove aportion of the first substrate; forming a deep interconnect trenchextending from the first interconnect structure to the secondinterconnect structure; and forming a backside deep contact (BDCT)feature in the deep interconnect trench, thereby electrically couplingthe logic device to the image sensor.
 17. The method of claim 16,wherein the first substrate includes: a first semiconductor layer; adielectric layer disposed over the first semiconductor layer; and asecond semiconductor layer disposed over the dielectric layer.
 18. Themethod of claim 17, wherein annealing the first substrate to therebyremove the portion of the first substrate includes removing the firstsemiconductor layer.
 19. The method of claim 18, further comprisingplanarizing the first substrate to remove the dielectric layer afterremoving the first semiconductor layer.
 20. The method of claim 16,further comprising: forming a passivation layer over the first substrateafter forming the BDCT feature; and coupling a third substrate to thefirst substrate after forming the passivation layer over the firstsubstrate.